Generally, fine pattern formation is carried out by the photolithography in manufacturing processes of a semiconductor device. A number of transfer masks (photomasks) are normally used for this fine pattern formation. The transfer mask comprises generally a transparent substrate having thereon a fine pattern made of a metal thin film or the like. The photolithography is used also in the manufacture of the transfer mask.
In the manufacture of a transfer mask by the photolithography, use is made of a mask blank having a thin film (e.g. light-shielding film or the like) for forming a transfer pattern (mask pattern) on a transparent substrate such as a glass substrate.
The manufacture of the transfer mask using the mask blank comprises an exposure process of applying required pattern writing to a resist film formed on the mask blank, a developing process of developing the resist film according to the required pattern writing to form a resist pattern, an etching process of etching the thin film according to the resist pattern, and a process of stripping and removing the remaining resist pattern.
In the developing process, a developer is supplied after applying the required pattern writing (exposure) to the resist film formed on the mask blank to dissolve a portion of the resist film soluble in the developer, thereby forming the resist pattern. In the etching process, using this resist pattern as a mask, an exposed portion of the thin film, where the resist pattern is not formed, is dissolved by dry etching or wet etching, thereby forming a required transfer pattern on the transparent substrate. In this manner, the transfer mask is manufactured.
For miniaturization of a pattern of a semiconductor device, it is necessary to shorten the wavelength of an exposure light source for use in the photolithography in addition to the miniaturization of the transfer pattern formed in the transfer mask. In recent years, the wavelength of an exposure light source in the manufacture of a semiconductor device has been shortened from KrF excimer laser (wavelength 248 nm) to ArF excimer laser (wavelength 193 nm).
As a type of transfer mask, a halftone phase shift mask is known apart from a conventional binary mask having a light-shielding film pattern made of a chromium-based material on a transparent substrate. This halftone phase shift mask is configured to have a light-semitransmitting film (halftone phase shift film) on a transparent substrate. This light-semitransmitting film is made of, for example, a material containing a molybdenum silicide compound or the like and is adapted to transmit light having an intensity that does not substantially contribute to exposure (e.g. 1% to 20% at an exposure wavelength) and to give a predetermined phase difference to this transmitted light. By means of light-semitransmitting portions formed by patterning the light-semitransmitting film and light-transmitting portions formed with no light-semitransmitting film and thus adapted to transmit exposure light, the halftone phase shift mask provides a relationship in which the phase of the light transmitted through the light-semitransmitting portions is substantially inverted with respect to the phase of the light transmitted through the light-transmitting portions (i.e. shifts the phase). As a consequence, the lights having passed near the boundaries between the light-semitransmitting portions and the light-transmitting portions and bent into the others' regions due to the diffraction phenomenon cancel each other out. This makes the light intensity at the boundaries approximately zero to thereby improve the contrast, i.e. the resolution, at the boundaries.
Further, in the exposure technique using ArF excimer laser (wavelength 193 nm) as exposure light, the miniaturization of a transfer pattern has advanced to require coping with the pattern line width which is smaller than the wavelength of the exposure light. As a consequence, there have been developed the resolution enhancement technology, such as the oblique illumination method and the phase shift method, and further the hyper-NA technique with NA=1 or more (immersion exposure etc.).
With the advance of transfer pattern miniaturization, the width of a resist pattern has been narrowed. Therefore, the aspect ratio becomes high with the thickness of a conventional resist film so that it is becoming difficult to form a transfer pattern by dry-etching a light-shielding film using the resist pattern as a mask.
As one means for solving this problem, there has been developed a binary mask blank having a structure in which a light-shielding film capable of being dry-etched with a fluorine-based gas is formed by a film containing a transition metal and silicon and an etching mask film made of a chromium-based material is formed on the light-shielding film (Patent Document 1). A method of manufacturing a transfer mask from this mask blank comprises first forming a resist pattern on the etching mask film and then using the resist pattern as a mask to carry out dry etching using a mixed gas of chlorine and oxygen as an etching gas, thereby forming a transfer pattern in the etching mask film. Then, using the transfer pattern of the etching mask film as a mask, dry etching is carried out using a fluorine-based gas as an etching as, thereby forming a transfer pattern in the light-shielding film. Then, the etching mask film is removed and, through a predetermined cleaning process, a binary transfer mask is manufactured.